1. Field of the Invention
The present invention concerns a telecommunication network for transmitting, receiving and switching digital data packets and, more particularly, a packet-switching network of the multiservice type. Multiservice packet networks serve to transmit, between multiservice subscribers, packets of digital data of different nature for example packetized speech data, visiophony image and sound data and digital information data. Such data originate from several digital data transmit equipments and are intended to digital data receive equipments, the said equipments being located in the subscriber's stations.
The object of the invention is to provide a packet switching network of the multiservice type in which the switching operations are made in real time, in the meaning that the packets are only stored long enough, in a switching unit, for the address of the packet to be read and the connection corresponding to said address to be set up.
The delay taken by a packet for going across a switching network comprises two parts, the first spent in reading out the switching address and the second in implementing the switching operation.
The principal object of the invention is to restrict the duration of the switching operation per se by decreasing the cases when the packet must be stored due to the occupation of the outgoing channel designated by the address.
2. Description of the Prior Art
French Patent No. FR-B-2242821 has disclosed a multiservice packetized telecommunication network comprising subscriber's stations and switching networks connected therebetween through packet transmit channels in which the packets comprise an information field and an address field. At the starting station of the packets, the address field is fulfilled with the address which in each switching network included in the route of the packet designates the number of the outgoing channel to which the incoming channel conveying the packet is to be connected. A pointer word marks the serial number of the address assigned to the first switching network to be encountered in the route and this pointer word is incremented by one unit when it has made its way through a switching network.
All the switching addresses of the switching networks included in the route remain in the address field of the packet during all its travel between calling and called subscribers. Further the packets are stored in incoming and outgoing stores in all the switching networks which they go through the whole network.
It is also known from Patent No. FR-B-2309088 to clear the switching address assigned to a switching network once the packet has been switched in said switching network. Thus, the fulfilled part of the address field of the packet has a decreasing number of bits as the packet goes along its route.
The multiservice packet telecommunication network of the invention comprises:
a plurality of subscriber's stations each connected to several sources of analog data signals and digital data signals and including means for digitizing said analog data signals from those of said sources which are analog data signal sources;
a plurality of means in each subscriber's station for forming, transmitting and receiving packets constituted by said digital data signals and said digitized data signals, said packets having an information field, an address field and a start word and end word fields, said start word field preceding said address field;
packet switching networks, each connected to said subscriber's stations and to other packet switching networks through incoming and outgoing data channels;
means for inserting in the address field of the packet a sequence of addresses including a first, second, . . . n.sup.th addresses defining the outgoing data link of the first, second, . . . n.sup.th switching networks included in the route of the packet between a packet sender station and a packet receiver station; and it is characterised in that the outgoing channel from each switching network towards other switching networks and the subscriber stations are associated in groups of a plurality of outgoing channels, the whole group having one and the same address common to all the channels of the group and the switching network further comprises
means (342A, 342B) for detecting said common address of a group in the address field of a packet conveyed in an incoming channel; and
means (344A, 344B) controlled by said address detecting means for searching a free non-addressed outgoing channel of the group, said searching means connecting said free outgoing channel to said incoming channel.